Apatitic phosphors such as Cool White haloapatite phosphors exhibit a decrease in brightness and relative quantum efficiency when their soluble antimony content increases much beyond 0.70 weight percent and they are fired in an inert atmosphere. A decrease in brightness also typically occurs when haloapatite phosphors are ball milled or attritor milled or otherwise particle size reduced. Since Cool White phosphors having higher soluble antimony content and finer particle sizes should, at least theoretically perform better in lamps at lower powder weights, it is desirable to offset any decrease in brightness due to increased antimony content or milling.
European Patent Application 0 239 924 to Gillooly et al describes a calcium halophosphate phosphor having the formulation Ca.sub.10-a-w-x Cd.sub.w Mn.sub.x Sb.sub.a (PO.sub.4).sub.6 F.sub.2-a-y Cl.sub.y O.sub.a where a is from 0.1 to 0.2, w is from 0 to 0.2, x is from 0.15 to 0.5, and y is from 0.03 to 0.3. As set forth in the specification, as compared to calcium halophosphate phosphor having an antimony content below about 0.10 mole per mole of phosphor, the process of the European Application modifies the synthesis of the phosphor. Phosphor synthesis is performed by utilizing a low oxygen content atmosphere, i.e. 50-5000 ppm, during both steps of a two step firing process. After the first firing, the phosphor is milled before the second firing. U.S. Pat. No. 4,806,824 describes a dual coat phosphor coating layer using the above phosphor.
U.S. Pat. No. 3,639,253 to Gillooly describes the preparation of an antimony-doped calcium pyrophosphate intermediate by reacting CaHPO.sub.4 and SbO.sub.3, and the resulting Ca.sub.2 P.sub.2 O.sub.3 xCa(SbO.sub.3).sub.2 is used along with, for example, CaCo.sub.3 and CaF.sub.2 to produce antimony-doped phosphors having a bluish color. Cool white and warm white phosphors can be produced as known the art by using CaCl.sub.2 and MnCO.sub.3 as additional ingredients. The firing technique utilizes open silica dishes in the presence of oxygen. A second firing step as discussed in the example utilizes an inert atmosphere such as nitrogen.